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ocamldumpobj misreports address operands of CLOSUREREC instructions #4563

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vicuna opened this Issue Jun 5, 2008 · 0 comments

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commented Jun 5, 2008

Original bug ID: 4563
Reporter: premchai21
Status: closed (set by @damiendoligez on 2008-09-10T12:53:37Z)
Resolution: fixed
Priority: normal
Severity: minor
Version: 3.10.2
Fixed in version: 3.11+dev
Category: ~DO NOT USE (was: OCaml general)
Monitored by: ines

Bug description

Compiling a file with the definitions:

let rec even x = if x == 0 then true else odd (x-1)
and odd x = if x == 0 then false else even (x-1)

and then running ocamldumpobj on the resulting object file yields
output containing the instruction:

  28  CLOSUREREC 0, 4294967298, 4294967311

which seems incorrect. From examining interp.c, CLOSUREREC seems to
take a count of variables and a number of function bytecode addresses,
and dumpobj.ml is outputting the operands in that order, but it's also
erroneously adding 2^32 to the addresses. E.g., the above line should
probably read:

  28  CLOSUREREC 0, 2, 15

Additional information

This is on Debian GNU/Linux, unstable variant, AMD64 architecture,
with OCaml 3.10.2, Debian OCaml package version 3.10.2-3. A glance at
tools/dumpobj.ml seems to indicate that what's happening is that the
offset is being treated as unsigned (comment mine for annotation):

    print_int nvars;
    for i = 0 to nfuncs - 1 do
      print_string ", ";
      print_int (orig + inputu ic);  (* <-- unsigned offset *)
    done;

This probably works on 32-bit machines because the Caml integers wrap
around properly in that case anyway, but on a 64-bit architecture,
there's more range in a Caml int and so treating the 32-bit offset as
an unsigned int rather than a signed one causes errors in bits 32 and
above in the result.

@vicuna vicuna closed this Sep 10, 2008

@vicuna vicuna added the bug label Mar 19, 2019

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